As for the oxide superconductor, a critical temperature (Tc) is high compared with a conventional metal system, superconductor such as Nb3Sn system, and the electric power cable, and applied equipments such as transformer, motor, and electric power storage system can be operated under the liquid nitrogen temperature. Therefore, the making of the wire rod is studied energetically. Especially, in RE3Ba2Cu3O7-y (here, RE3 shows any one kind or more than two kinds of elements selected from Y, Gd, Sm, Nd, Ho, Dy, Eu, Tb, Er, Yb, and hereinafter called RE3BCO) superconductor, because the attenuation of the conducting current is small in the high magnetic field area, that is, because the magnetic-field property in the liquid nitrogen temperature is excellent compared with Bi system superconductor, the practical high critical current density (Jc) can be maintained. And, in addition to the excellent property in the high temperature area, because the manufacturing method which does not use silver of the precious metal is possible and the liquid nitrogen can be used as the refrigerant, the cooling efficiency improves remarkably. Therefore, it is extremely advantageous economically and the making of the wire rod is expected as the next-generation superconducting material.
Generally, the RE3BCO oxide superconducting wire rod has the structure that at least one layer or a plurality of layers of the biaxially-oriented oxide layer are formed onto the metallic substrate, and the oxide superconducting layer is formed onto it, and further, the stabilizing layer which undertakes the role as the surface protection of the superconducting layer, the improvement of the electric contact, and the protection circuit at the time of the excessive energization is stacked. In this case, it is known that the critical current property of the RE3BCO wire rod depends on the in-plane orientation of the superconducting layer, and is influenced greatly by the intermediate layer which becomes the basic material and by the in-plane orientation and the smooth surface property of the oriented metallic substrate.
The crystal system of the RE3BCO oxide superconductor is the rhombic crystal, and because the lengths of three sides of x axis, y axis and z axis are different and the angles among the three sides of the unit cell are also slightly different respectively, it is easy to form the twin crystal. And because the slight gap of the azimuth generates the twin crystal grain boundary and reduces the conducting property, to bring out the property of the material in the conducting state, in addition to alignment of the CuO face of the inside of the crystal, the alignment of the crystal orientation in the in-plane also is demanded. Therefore, the making of the wire rod has the difficulty compared with the Bi system oxide superconductor.
The manufacturing method of the making of the wire rod which improves the in-plane orientation of the crystal of the RE3BCO oxide superconductor and aligns the azimuth direction in the in-plane is same as the manufacturing method of the thin film. That is, the intermediate layer whose in-plane orientation and azimuth direction are improved is formed onto the tape-shaped metallic substrate, and the crystal lattice of this intermediate layer is used as the template. And thereby, the in-plane orientation and the azimuth direction of the crystal of the Re3BCO oxide superconducting layer are improved.
The RE3BCO oxide superconductor is studied in various manufacturing processes now, and various biaxially-oriented composite substrates which form the in-plane oriented intermediate layer onto the tape-shaped metallic substrate are known.
Among these, at present, the process which shows the highest critical current property is a method of using the IBAD (Ion Beam Assisted Deposition) substrate. In this method, onto the polycrystalline non-magnetic and high strength tape-shaped Ni system substrate (hastelloy etc.), the particle generated from the target while irradiating the ion from a direction of the constant angle for the normal line of this Ni system substrate is deposited by pulsed laser deposition (PLD) method. And, the intermediate layer (CeO2, Y2O3, YSZ etc.) or the intermediate layer of the double-layered structure (YSZ or RxZr2O7/CeO2 or Y2O3 etc.: Rx shows Y, Nd, Sm, Gd, Eu, Yb, Ho, Tm, Dy, Ce, La or Er) which has the fine grain size and the high orientation and inhibits the reaction with the element which composes the superconductor is formed. And, after forming the CeO2 film onto it by PLD method, in addition, YBa2Cu3O7-y (hereinafter called YBCO) layer is formed by PLD method or CVD method, and the superconducting wire rod is formed (for example, refer to Patent document No. 1 to No. 3).
However, in this process, because all intermediate layers are formed by the vacuum process in the gas phase method, although this process has the advantage that the dense and smooth intermediate layer film can be obtained, there are problems that the production speed is slow and the production cost rises. Although the processes of forming films by using some gas phase methods other than this IBAD method have been studied, the effective means which solve the problems of the production speed and the production cost have not been reported.
The most effective process for attaining the low cost is the MOD process where the organic acid salt or the organic metallic compound is used as the raw material and the oxide layer is formed by giving the thermal decomposition and the crystallization heat-treatment after coating this solution onto the surface of the substrate. Although this process is simple, because the long time heat-treatment in high temperature is necessary, by the generation of cracks due to the contraction in volume of film at the time of the thermal decomposition, the non-uniform reaction by the imperfect of grain growth, and the decrease of the crystalline by such as the diffusion through the crystal grain boundary of the metallic element which composes the substrate, it was difficult to obtain the film having the function enough as the intermediate layer.
Generally, as the intermediate layer of the superconductor, especially in the case of YBCO, although CeO2 which is formed by PVD method is used as described above, because CeO2 intermediate layer is excellent in the lattice consistency with the YBCO layer and in the oxidation resistance, and because the reactive property with the YBCO layer is small, this depends on what is known as one of the most excellent intermediate layer. When this CeO2 intermediate layer is formed by MOD method, the cracks are generated due to the large difference of the coefficient of thermal expansion with the metal of the substrate, and it becomes impossible to accomplish the function as the intermediate layer. When the film is formed by MOD method onto the Ni substrate by the solid solution that Gd is added to CeO2, although the generation of cracks is inhibited by being able to alleviate the difference of the coefficient of thermal expansion, because the diffusion of the element from Ni or Ni alloy substrate cannot be stopped in the inside of the intermediate layer, there was a problem that the superconducting property decreases.
In order to prevent the diffusion of the element which composes this substrate, the study of the intermediate layer material (Ce2Zr2O7) that a part of CeO2 is substituted to Zr is carried out. And for example, in the oxide superconductor that one layer or a plurality of layers of the biaxially-oriented intermediate layer by the inorganic material is formed and the oxide superconducting layer is provided onto this, by providing the intermediate layer which includes one kind of element selected from Ce, Gd or Sm and Zr onto the above-mentioned substrate, the effect of preventing the diffusion to the superconducting layer of the metallic element which composes the substrate is admitted, and the property of Jc>1MA/cm2 is obtained (refer to Patent application No. 2005-306696 and Patent application No. 2005-360788).    Patent document No. 1: Japanese Patent Publication No. Hei04-329867    Patent document No. 2: Japanese Patent Publication No. Hei04-331795    Patent document No. 3: Japanese Patent Publication No. 2002-203439